1. Field of the Invention
The present invention relates to a heat resistant resin composition for sealing semiconductors, and particularly to a resin composition suitable for sealing semiconductor devices in which high heat resistance is required, as in, for example, surface mounting semiconductor devices, semiconductors used at high temperatures, etc.
2. Description of the Prior Art
There is a trend to implement high density mounting in the fields of electric apparatuses, electronic parts, particularly semiconductors, and it has been necessary to develop a resin composition having high heat resistance to heat released during mounting or while being used.
Sealing with a resin has conventionally been carried out by transfer molding useing an epoxy resin from the standpoint of economy, and at present particularly a combined system of o-cresol novolac epoxy resin and a novolac phenol resin as a curing agent has predominantly been used because of high moisture resistance.
However, there is a tendency for the resin-sealing semiconductor device to shift to a surface mounting semiconductor device by following the trend of the above high density mounting. Different from the insertion semiconductor device, according to the surface mounting semiconductor, a package is exposed as a whole to a soldering temperature of 200.degree. C. or higher. Additionally, the semiconductor devices are used at high temperatures for a long period of time as in around the automobile engine. Such a high heat resistance to the above high temperatures is demanded for the resin composition as the sealing material, and it has become impossible for the conventional epoxy resin to satisfy the above demand.
Therefore, attempts to increase the density of crosslinking have been made for the purpose of increasing the glass transition temperature. However, a simple increase in crosslink density causes such problems as an increase degree of water absorption of the resin and impairment of flexibility. An increase in degree of water absorption results in reduction in heat resistance and particularly in an increase of solder crack development at the time of moisture absorption, and a reduction in flexibility results in an increase of internal stress and in a reduction in thermal shock resistance.